The present invention relates to over-the-road trailer vehicles for transporting relatively long and heavy loads and more particularly to a special coupling for interconnecting of an auxiliary extension axle apparatus to a main frame of a trailer assembly for supporting and distributing the total load weight throughout additional axles of the main trailer and the extension axle apparatus.
In over-the-road and off-road transport of various long and heavy loads, such as large earth working equipment, building equipment and machinery, building components and other long and heavy loads, a tractor/trailer unit is used. The trailer of the tractor/trailer unit includes a trailer bed for carrying the load which includes a king pin connection at one end for attachment to the main frame of a tractor or other power unit. One or more set of rearwardly spaced and generally tandem rear axles and supporting wheels are secured to the back end of the trailer for supporting the rear of the bed and the load thereon. The weight of the load must be distributed between the various wheeled supports of the tractor and the trailer within governmental established weight limits per axle for over-the-road transport on public roads. With various long and heavy loads, further wheeled support must Often be provided for distribution of the overall load weight in order to meet jurisdictional and governmental requirements with respect to axle loading on the roadway. Rather than providing a completely separate trailer structure, the industry has developed load extension axle apparatus to provide for further distribution of the load beyond the rear of the standard trailer.
Various booster or extension axle units have been suggested in the prior art. The prior art devices generally consist of a forward connecting arm member which generally includes a pivotal interconnection of the extension axle unit to the trailing end of the main trailer. The pivotal connection is provided to permit turning of the axle unit relative to the main trailer, and may also permit vertical pivotal movement of the extension axle unit relative to the main trailer. The relative vertical movement of the assembly has to be carefully considered and designed to permit movement of the loaded trailer unit over uneven terrain including ditches, raised or humped portions and the like.
For example, U.S. Pat. No. 4,423,884 issued Jan. 3, 1984 to Gevers discloses a particular axle extender construction including an adjustable pivot connection between a booster axle connecting member and the main frame of the trailer. U.S. Pat. No. 4,741,549 issued May 3, 1988 discloses another extender construction with vertical pivotal turning pin connector. U.S. Pat. No. 3,580,608 which issued May 25, 1971, discloses a direct coupling of a small trailer to a vehicle with a spaced parallel arm assembly to position a trailer relative to the vehicle for pulling a four wheel trailer. The patent discloses the usual pivot hinge connection to a vehicle for pulling of the trailer.
Similarly, certain locations and areas may require air-cushion support for the extender axle wheels but mechanical supports are also often used. The air-cushion support allows convenient vertical orientation of the bed of the extender unit for proper location with respect to the load and the road. Shinning of the load with respect to the extender may be provided in accordance with the relative orientation of the load with respect to the load extender and the distribution requirements. The various requirements and variations in the extender positioning, which is required because of the different loads encountered, have generally required special construction to permit assembly to accommodate the various loads.
Generally, the principle problems which have been encountered with prior art systems involve maintaining the extension axle unit level and with a constant load as the axle unit moves over uneven terrain and actual tipping of the trailer and load during turning of the tractor/trailer assembly. The load characteristic is primarily the need for extension coupling mechanism in which the extension frame is moved to a proper position to carry the load, while the vertical pivot pin coupling for turning creates adverse tipping forces on the trailer assembly during turning of the tractor/trailer assembly can tip the trailer and load onto its side.
Although various suggestions have been incorporated in prior art structures, there is a continuing need for a reliable structure which will provide improved movement of the load over uneven road and terrain environments.